1. Technical Field
The present invention relates to a circuit structure, and more particularly, to a circuit structure with tunable resistors or capacitors.
2. Background
Demand for mixed-mode integrated circuits (ICs) including data converters, analog-to-digital/digital-to-analog converters, and digital radio chips is rapidly increasing. With the advent of cellular technology and network technology this category now further includes cellular telephone, software radio, LAN, and WAN router ICs. From the fabrication viewpoint, semiconductor process technology has been continually scaling down for the past four decades and the trend continues, where CMOS technology is usually optimal for digital performance and scaling while bipolar transistors are usually optimal for analog performance. However, until the last decade it was difficult to either combine these cost-efficiently or to include both analog and digital in a single design without serious performance compromises. In one aspect, reduced scales of process geometries, combined with the increasing number of resistors and capacitors at each new process node, are forcing the development of a new IC design that fits more circuit elements on fixed or shrinking IC real estate. Conventional capacitors in ICs are parallel plate capacitors, using high dielectric strength materials including SiO2 dry oxide, polysilicon oxide, or Si3N4 CVD oxide in a variety of electrode combination settings (for example, metal-metal, poly-poly, metal-poly, metal-diffusion, poly-diffusion, etc.). Conventional resistors in ICs are made of strips of resistive layer with contacts and surrounding isolation. To achieve large resistance, the adoption of long strips with large length-to-width ratios is unavoidable. The conventional capacitor and resistors are both based on a planar/horizontal design rule that consumes precious IC real estate. To resolve such issue, a new design concept based on vertically integrated resistors and capacitors is disclosed in the present invention.